JP2564510B2 - Abnormality detection method for exhaust gas concentration sensor of internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for detecting an abnormality in an exhaust gas concentration sensor of a fuel supply control device, which feedback-controls an air-fuel ratio according to an output signal of an exhaust gas concentration sensor of an internal combustion engine. In particular, the present invention relates to an abnormality detection method for detecting an abnormality of an exhaust gas concentration sensor from a change in an output signal of the exhaust gas concentration sensor.

(Technical background of the invention and its problems) Generally, in order to control the air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine to fall within a certain range around a desired value, it is included in exhaust gas. A specific component concentration, such as an oxygen gas concentration, is detected, an air-fuel ratio correction coefficient value is set according to the detected oxygen gas concentration, and the air-fuel ratio is corrected using this correction coefficient value. An oxygen gas concentration sensor (hereinafter referred to as an O ₂ sensor) which is an exhaust gas concentration sensor for detecting the oxygen gas concentration from the exhaust gas of an internal combustion engine is, for example, of a type including a zirconia solid electrolyte (ZrO ₂ ). The electromotive force has a characteristic that it rapidly changes before and after the stoichiometric air-fuel ratio of the internal combustion engine, and the output signal of the O ₂ sensor has a high level on the exhaust gas rich side and a low level on the lean side. The disconnection or deterioration of the O ₂ sensor for detecting the oxygen gas concentration has a great influence on the air-fuel ratio control. For this reason, it is necessary to constantly monitor an exhaust gas concentration detection system including an exhaust gas concentration sensor such as an O ₂ sensor and make the air-fuel ratio control system function normally with a normal sensor signal.

As a method for detecting an abnormality in the exhaust gas concentration sensor for that purpose, conventionally, the time interval from the time when the correction coefficient value changes stepwise to the time when it next changes stepwise, that is, the reversal time interval from the rich side to the lean side or vice versa. When the measured time interval is equal to or longer than a preset time, it is determined that the exhaust gas concentration sensor has an abnormality, and when the abnormality is detected, the correction coefficient value is set to a predetermined value and the exhaust gas is set. Japanese Patent Application Laid-Open No. Sho-Atsu, which is designed to detect an abnormality in the density sensor.
Known by issue number 58-222939.

Further, when the correction coefficient value is out of the normal value range defined by the upper and lower limit values that can be taken during normal operation of the engine, the elapsed time from the time when the correction coefficient value is out of the normal value range is measured, and the measured elapsed time Is a method for determining that the exhaust gas concentration sensor is abnormal when the time exceeds a predetermined time.
-3137. However, since this is also that of any conventional abnormality detection method, during low load operation including idling of the engine, the temperature of the O ₂ sensor whose activation is not sufficiently performed low, the O ₂ There is a possibility that the output voltage level of the sensor becomes unstable and a rich signal or lean signal different from the actual air-fuel ratio is output, and normal air-fuel ratio feedback control may not be performed. If an abnormality is detected in the exhaust gas concentration sensor in this state, there is a problem that the exhaust gas concentration sensor such as the O ₂ sensor may be erroneously diagnosed as abnormal although it is actually normal.

Furthermore, the output voltage from the exhaust gas concentration sensor is 6 V, for example.
An abnormality detecting method for determining that the exhaust gas concentration sensor is abnormal when the above high voltage is known is known from JP-A-53-95431. However, the exhaust gas concentration sensor in the conventional way, i.e. O ₂ can detect a disconnection of the sensor, since when the O ₂ sensor is short-circuited decreases the output voltage is 0, the abnormality due to the short circuit of the O ₂ sensor It could not be detected.

(Object of the Invention) The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an abnormality detection method for an exhaust gas concentration sensor of an internal combustion engine, which is capable of early and surely detecting an abnormality of an O ₂ sensor. To aim.

(Means for Solving the Problems) In order to solve the above problems, according to the present invention, the air-fuel ratio correction is set according to the output signal of the exhaust gas concentration sensor for detecting the exhaust gas concentration of the internal combustion engine. In an abnormality detection method for an exhaust gas concentration sensor of an internal combustion engine, which comprises a fuel supply control device that feedback-controls the amount of fuel supplied to the internal combustion engine based on a value, the first predetermined time elapses after the engine is started, and When the output signal is read and stored, and the output signal does not change for a second predetermined time that starts after the first predetermined time has elapsed and before the activation of the exhaust gas concentration sensor is completed, the exhaust gas There is provided a method for detecting an abnormality in an exhaust gas concentration sensor of an internal combustion engine, which is characterized by determining that the concentration sensor is abnormal.

Embodiments of the Invention Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the overall configuration of a fuel supply control device for an internal combustion engine to which the abnormality detection method of the present invention is applied. Reference numeral 1 denotes, for example, a four-cylinder internal combustion engine, an intake pipe 2 is connected to the engine 1, and a throttle valve 3 is provided in the middle of the intake pipe 2. The throttle valve 3 is connected to a throttle valve opening sensor 4 which detects the valve opening θ _TH and outputs an electrical signal. The detected throttle valve opening signal is as described below. Then, it is sent to an electronic control unit (hereinafter referred to as "ECU") 5 that executes arithmetic processing for calculating the air-fuel ratio and the like and abnormality detection processing for the exhaust gas concentration sensor.

A fuel injection valve 6 is provided between the engine 1 and the throttle valve 3. The fuel injection valve 6 is provided for each cylinder of the engine 1, is connected to a fuel pump (not shown), and controls a valve opening time for injecting fuel by a drive signal supplied from the ECU 5.

On the other hand, an intake pipe absolute pressure sensor 8 for detecting the absolute pressure P _BA in the intake pipe 2 is connected to the intake pipe 2 downstream of the throttle valve 3 via a pipe 7, and the detection signal thereof is EC.
Sent to U5. Further, an intake air temperature sensor 9 for detecting an intake air temperature (T _A ) is attached to the intake pipe 2 downstream of the pipe 7,
The detection signal is sent to the ECU 5.

The cylinder 1 of the engine 1, which is filled with cooling water, is provided with a thermistor, for example, on the cylinder peripheral wall, and the temperature of the cooling water (T _W )
An engine cooling water temperature sensor 10 for detecting the above is provided, and the detection signal thereof is sent to the ECU 5. An engine speed sensor (hereinafter referred to as Ne sensor) 11 and a cylinder discrimination (CYL) sensor 12 are mounted around a cam shaft or a crank shaft (not shown) of the engine 1, and the former Ne sensor 11 is 180 ° of the crank shaft. A signal of 1 pulse is output for each rotation, and the latter cylinder discrimination sensor 12 outputs 1 pulse of a signal for discriminating a cylinder at a predetermined angular position of the crankshaft, and these pulse signals are sent to the ECU 5.

A three-way catalyst 14 is connected to the exhaust pipe 13 of the engine 1 to purify HC, CO and NO _X components in the exhaust gas. An O ₂ sensor 15, which is an exhaust gas concentration sensor, is attached to the exhaust pipe 13 on the upstream side of the three-way catalyst 14, and the O ₂ sensor 15 detects the oxygen gas concentration in the exhaust gas and outputs the detection signal thereof. EC
Supplying to U5.

Further, another engine operating parameter sensor, for example, an atmospheric pressure sensor 16 is connected to the ECU 5, and the atmospheric pressure sensor 16 supplies a detection signal thereof to the ECU 5. The ECU5
Inputs the above various signals and calculates the fuel injection time T _OUT of the fuel injection valve 6 by the following equation.

T _OUT = Ti × KO ₂ × K ₁ × K ₂ (1) where Ti is the reference injection time of the fuel injection valve 6, and the engine speed Ne detected by the Ne sensor 11 and the intake pipe It is calculated according to the absolute pressure signal P _BA from the absolute pressure sensor 8. K _O2 is an air-fuel ratio correction coefficient, which is set according to the oxygen gas concentration indicated by the detection signal of the O ₂ sensor 15 during feedback control, and is set during feedback control during open-loop control. It is set to the average value K _REF of the numerical value K _O2 .

K ₁ and K ₂ are various sensors described above, that is, the throttle valve opening sensor 4, the intake pipe absolute pressure sensor 8, the intake air temperature sensor 9, the engine cooling water temperature sensor 10, the Ne sensor 11, the cylinder discrimination sensor 12, O _2. A correction coefficient or a correction variable calculated according to the engine parameter signal from the sensor 15 and the atmospheric pressure sensor 16, which includes a starting characteristic, an exhaust gas characteristic, a fuel consumption characteristic, an engine acceleration characteristic, etc. according to the operating state of the engine 1. The calculation is performed based on a predetermined calculation formula so that the various characteristics are optimized.

The ECU 5 uses the fuel injection time T calculated by the equation (1).
_A drive control signal based on _OUT is supplied to the fuel injection valve 6 to control the valve opening time.

FIG. 2 is a block diagram showing the internal configuration of the ECU 5 shown in FIG. The engine speed signal from the Ne sensor 11 in FIG. 1 is waveform-shaped by the waveform shaping circuit 501, and then the top dead center (T
The signal is supplied to a central processing unit (hereinafter referred to as a CPU) 503 as a DC) signal, and is also supplied to a Me counter 502. The M
The e counter 502 counts the pulse generation time interval between the previous pulse and the current pulse of the TDC signal, and the resulting count value Me is proportional to the reciprocal of the engine speed Ne.
The Me counter 502 sends this count value Me to the CP via the bus 510.
Supply to U503.

1, the throttle valve opening sensor 4, the intake pipe absolute pressure sensor 8, the engine cooling water temperature sensor 10, the O ₂ sensor 15
The respective output signals from the above are corrected to a predetermined voltage level by the level correction circuit 504, and then sequentially supplied to the A / D converter 506 by the multiplexer 505. The A / D converter 5
06 sequentially converts the output signals from the above-mentioned sensors into digital signals and supplies the digital signals to the CPU 503 via the bus 510.

The CPU 503 is further connected to a read-on memory (hereinafter referred to as ROM) 507, a random access memory (hereinafter referred to as RAM) 508, and a drive circuit 509 via the bus 510. The ROM 507 stores various programs executed by the CPU 503 such as an exhaust gas concentration sensor abnormality determination program shown in FIG. 3 described later, various data and tables such as a reference injection time Ti and an abnormality determination value ΔV ₀₂ described later. are doing. The RAM 508 is the result of the operation executed by the CPU 503,
It is used when temporarily storing the data read from the Me counter 502 and the A / D converter 506. The drive circuit 509 receives the fuel injection time T _OUT calculated by the equation (1), and supplies the fuel injection valve 6 with a drive signal for opening the fuel injection valve 6 for the time indicated by this.

FIG. 4 is an output voltage characteristic diagram of the O ₂ sensor 15 after the ignition switch of the engine is turned on. Output voltage V _O2 of the O ₂ sensor 15, immediately after ON of the ignition switch is a low-pass filter of the O ₂ sensor input circuit interposed between the first 5 O ₂ sensor 15 as shown in FIG ECU5 Due to the capacitors C ₁ and C ₂ and the resistor R, the voltage rises from OV to around 3.5V with some time delay. After that, as the activation of the O ₂ sensor progresses, the output voltage V _O2 gradually decreases, and the activation of the O ₂ sensor is completed near OV (time T in FIG. 4). After that, when the O ₂ sensor is normal, the output voltage V _O2 becomes high level (0.9 V) if the oxygen concentration in the exhaust gas is rich, and becomes low level (0.1 V) if it is lean. On the other hand, when a disconnection occurs in the O ₂ sensor 15, the output voltage V _O2 is maintained at a constant high voltage (about 3.5V) as shown by the dotted line I, and when the O ₂ sensor 15 is short-circuited, the output voltage is reduced. The voltage V _O2 does not rise and is maintained near OV as shown by the dotted line II.

FIG. 3 is a flow chart of abnormality detection processing by the O ₂ sensor abnormality detection method of the present invention. This process is CPU503
Is executed every time the TDC signal is generated.
First, in step 301, the ignition switch is set to O.
It is determined whether the FF state is changed to the ON state, and if the answer is affirmative (Yes), the abnormality detection flag O ₂ F _SB is set to 1 (step 302), and the process proceeds to the next step 303. If the determination result of step 301 is negative (No), the process immediately proceeds to step 303.

In step 303, it is determined whether or not a predetermined time t _O2 (for example, 5 seconds) corresponding to the rising delay of the low-pass filter shown in FIG. 5 has passed since the ignition switch was turned on. If this determination result is affirmative (Yes), the output voltage V _O2 of the O ₂ sensor 15 is read and stored as a V _O2FS value, and if negative (No), the process immediately proceeds to step 305.
As a result, the V _O2FS value is the voltage V ₁ when the O ₂ sensor 15 is normal,
The voltage is V ₁ ′ when the wire is broken and V ₁ ″ when the wire is short-circuited (see FIG. 4).

In step 305, it is determined whether or not the first and second flags N _FS1 and N _FS2 for abnormality determination are both set to the value 1, and if the answer is negative (No), step 306
Proceed to. In step 306, it is determined whether or not the abnormality detection flag O ₂ F _SB is set to 1 in step 302, and if the answer is affirmative (Yes), the process proceeds to the next step 307.
In step 307, it is determined whether or not the engine cranking is completed, that is, whether or not the engine speed Ne is higher than a predetermined cranking speed N _CR that enables the O ₂ sensor to be abnormally determined. Is positive (Yes), the process proceeds to the next step 308.

If the determination result of step 306 or 307 is negative (No), the t _O2FS timer used in step 310 to be described later is reset (step 309) and this program ends.

After step 308, the output voltage V _O2 of the O ₂ sensor 15 is verified. First, in step 308, the output voltage V _O2
Is approximately equal to the V _O2FS value, that is, V _O2 is V _O2FS ±
It is determined whether or not it is within ΔV _O2 . This value ΔV _O2 is the output voltage V _O2 for each TDC signal generation when the O ₂ sensor is normal.
Is set to a value smaller than the change amount of (for example, 0.1 V). If the answer is affirmative (Yes), whether or not the determination result of step 308 is continuously affirmative (Yes) until the predetermined timer time (for example, 600 seconds) of the t _O2FS timer elapses. It is determined whether or not the route has been continued and the _vehicle has passed the predetermined time t _O2FS (step 310). When the O ₂ sensor 15 is broken or short-circuited and the output voltage V _O2 is kept constant for a predetermined time t _O2FS as shown by the dotted line I or II in FIG. 4, the determination in steps 308 and 310 is performed. Both answers are affirmative (Yes).

If the determination result in step 310 is affirmative (Yes), it is determined in the next step 311 whether or not the first flag N _FS1 is set to 1, and if the answer is negative (No), the first 1
Flag N _FS1 is set to 1 (step 312) and t _O2FS
The timer is reset (step 313) and this program ends. If the determination result of step 311 is affirmative (Yes), the second flag N _FS2 is set to 1 (step 31
4), end this program. By setting the second flag N _FS2 in step 314, the determination result of step 305 in the next loop becomes affirmative (Yes), that is, O ₂
The abnormality of the sensor 15 is finally discriminated, and thereafter, the abnormality detection flag O ₂ F _SB is reset to 0 (step 315), the LED for abnormality alarm is displayed (step 316), and this program is terminated. . Thus, the two flags N _FS1 and N _FS1
Since both _FS2 of the O ₂ sensor 15 beginning when it is set to the value 1 is diagnosed to be abnormal, even one of the flag by mistake due to noise or the like is set to the value 1 O ₂
It is possible to detect the abnormality more reliably without misdiagnosing the sensor 15 as an abnormality.

On the other hand, when the determination result of step 308 is negative (No), that is, when the predetermined time t _O2 has passed and the rise of the output voltage V _O2 of the O ₂ sensor 15 is completed, the output voltage V _{O2 is set} to the normal state of the O ₂ sensor. If a change appears, it means that the O ₂ sensor 15 is normal (see FIG. 4) and resets the t _O2FS timer (step
317), The abnormality detection flag O ₂ F _SB is reset to 0, and this program ends.

As described above, O ₂ sensor 15 abnormality detection, O ₂ sensor 15 can be performed prior to the activation (T time previous Figure 4). Therefore, after the engine is started, the O ₂ sensor 1
It is possible to shorten the time until the abnormality 5 is detected and prevent deterioration of the exhaust gas purification performance of the engine.

(Effects of the Invention) As described in detail above, according to the abnormality detection method for the exhaust gas concentration sensor of the internal combustion engine of the present invention, according to the output signal of the exhaust gas concentration sensor for detecting the exhaust gas concentration of the internal combustion engine. A method for detecting an abnormality in an exhaust gas concentration sensor of an internal combustion engine, comprising: a fuel supply control device that feedback-controls a fuel amount supplied to the internal combustion engine based on a set air-fuel ratio correction value; After a lapse of a predetermined time, the output signal is read and stored, and the output signal changes for a second predetermined time that starts after the first predetermined time has elapsed and before the activation of the exhaust gas concentration sensor is completed. If not, it is determined that the exhaust gas concentration sensor is abnormal, so it is possible to detect an abnormality in the exhaust gas concentration sensor earlier than before. At the same time, it is possible to detect both abnormalities in the exhaust gas concentration sensor, including disconnection and short circuit. As a result,
If the time until the abnormality of the exhaust gas concentration sensor is detected after the engine is started is long, the exhaust gas purification performance may deteriorate during that time, but such a problem can be eliminated.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of a fuel supply control device for an internal combustion engine in which an abnormality detection method for an exhaust gas concentration sensor according to the present invention is implemented, and FIG. 2 is an electronic control unit (ECU) shown in FIG. FIG. 3 is a block diagram showing the configuration, FIG. 3 is a flow chart showing an abnormality detection procedure of the exhaust gas concentration sensor of the present invention, FIG. 4 is an output voltage characteristic diagram of the O ₂ sensor (exhaust gas concentration sensor), and FIG. 5 is O ₂ It is an input circuit diagram of a sensor. 1 ... Internal combustion engine, 2 ... Intake pipe, 5 ... Electronic control unit (ECU), 6 ... Fuel injection valve, 11 ... Engine speed sensor, 12 ... Cylinder discrimination sensor, 13 ... Exhaust pipe, 15 …… Oxygen (O ₂ ) sensor (exhaust gas concentration sensor), 503 …… CPU, 507 …… ROM, 508 …… RAM, 509 ……
Drive circuit.

Claims (1)

(57) [Claims] 1. A fuel supply control device for feedback controlling the amount of fuel supplied to the internal combustion engine based on an air-fuel ratio correction value set according to an output signal of an exhaust gas concentration sensor for detecting the exhaust gas concentration of the internal combustion engine. In an abnormality detection method for an exhaust gas concentration sensor of an internal combustion engine, the output signal is read and stored after a lapse of a first predetermined time after the engine is started, and the output signal is started after the lapse of the first predetermined time. An exhaust gas concentration of an internal combustion engine, wherein when the output signal does not change for a second predetermined time period before activation of the exhaust gas concentration sensor is completed, it is determined that the exhaust gas concentration sensor is abnormal. Sensor abnormality detection method.